[olug] Crossover cable communication

[Dave Burchell]

ERIC MAHLAKO says:
> 
> Hi there.
> 
> I want to have the following network setup, but I
> don't know how to setup my linux machines to support
> communication crossover cable.
> 
> Host1 <===> Router <====> Host2
> 
> I can ping Host1 with Host2 via the router and vice
> versa using a hub meaning my routing tables are setup
> correctly. The problem is that when I connect the
> three computers using crossover cable I can not ping
> any computer.
> 
> Can anyone help me with this problem, maybe there is
> something missing to be done to all the computers in
> order to support communication with crossover cable.
> 
> Thanks
> Lericom  

Hi Eric,

How is your network configured when it is working?

You don't need to do anything special to the computers to use a
crossover cable.  The crossover cable can be used to build an
ethernet segment of only two computers.  It should work just as if you
had plugged the two ethernet devices (computers, usually) into a hub
with ordinary cables.

(In my ASCII diagrams, the "<=====>" means an ordinary cable, and "<~~~~~>"
means a crossover cable.)

What does your network look like when it works with hubs?  Like this?

[A]  Host1 <======> HUB <=====> Router <======> HUB <======> Host2

If so, you should be able to replace the hubs with crossover cables, like
this:

[B]  Host1 <~~~~~~~~~~~~~~~~~~> Router <~~~~~~~~~~~~~~~~~~~> Host2

However, you only mentioned one hub.  If you have only one hub, you may
have connected your network like this when it was working:

[C]  Host1 <==================>  HUB  <====================> Host2
                                  ^
                                  =
                                  ===========> Router

There is no way (AFAIK) to eliminate the need for a hub by using
crossover cables if you have an ethernet segment of three or more
devices.  Does your network look like diagram [C] when everything is
working?

If you can make the network work the way you want it to when connected
like diagram [A] above, then replacing the hubs with crossover cables
should work just as well.  Try replacing one hub at a time with the
crossover cable, then testing that everything still works as you
expect; you could simply have a bad crossover cable.

-- 
Dave Burchell                                          40.49'N, 96.41'W
Free your mind and your software will follow.              402-467-1619
http://incolor.inetnebr.com/burchell/                  burchell at acm.org